STC8 microcontroller P5.4 / RST pin functionality

STC8 microcontrollers have P5.4 which can (optionally) be used as device reset pin.

STC calls is a low-level reset pin, but in more standard terminology, it is an active-low reset pin

In order to select between using P5.4 as a ~RST pin or just a GPIO port (P5.4), set or unset bit P54RST (bit 4) in the RSTCFG register.

  • If bit P54RST is unset (binary 0), pin P5.4 can be used as a normal GPIO pin, the RST functionality is disabled
  • If bit P54RST is set (binary 1), pin P5.4 is used as a RST pin. It can’t be used as a normal GPIO pin in this mode


Source: STC8G Datasheet, section 6.3.3+